Recent years have witnessed the growing importance of secondary batteries, such as lithium secondary batteries and nickel-hydride batteries, as vehicle-mounted power sources having electricity as a drive source, as well as in power sources provided in, for instance, portable terminals and other electronic devices. In particular, lithium secondary batteries (typically lithium ion batteries) that are lightweight and afford high energy density are expected to be used as preferred high-output power sources installed in vehicles (for instance, automobiles, in particular hybrid automobiles and electric automobiles).
Batteries that afford good electric performance over long periods of time, i.e. batteries having superior durability (cycle characteristic), are demanded in lithium secondary batteries, as the abovementioned vehicle-mounted high-output power source, that have a configuration wherein rapid charge and discharge (so-called high-rate charge and discharge) are performed repeatedly. One issue being addressed regarding the above demand relates to the improvement of the structure of electrode mix layers (positive electrode mix layer and negative electrode mix layer) that are capable of reversibly storing and releasing charge carriers (lithium ions) and that are formed on the surface of an electrode collector, in such a manner so as to achieve a better high-rate characteristic and cycle characteristic.
Patent Literature 1 is an instance of a prior art document concerned with the structure of a positive electrode mix layer in that kind of lithium secondary batteries. Patent Literature 1 aims at enhancing the low-temperature characteristic of a battery by setting a predetermined range of the pore size of a positive electrode mix layer, or of the pore volume per unit weight of a positive electrode active material in the positive electrode mix layer. Patent Literature 2 and Patent Literature 3 are concerned, among other features, with the pore distribution of positive electrode active materials that make up a positive electrode mix layer.